The broad objectives of this research are to characterize rat bone non- collagenous proteins that are made and secreted by osteoblasts and are found in the calcified matrix of bone and to determine their functions. The fundamental hypothesis on which these studies is based is that these NCPs are involved in the formation of bone. The recent demonstration that two of the bone matrix proteins are cell attachment proteins while others are growth factors indicate that some of the bone NPCs have activities relating to cells. The specific objectives of this research are: 1) to use antibodies against bone matrix proteins as markers to study osteoblast differentiation, 2) to determine the nature, location and biosynthesis of the post-translational modifications of osteopontin, a phosphorylated cell attachment protein, 3) to identify and characterize putative proteins linking osteopontin to the organic matrix of bone (type I collagen) 4) to continue studies on the characterization, biosynthesis and immunolocalization of newly discovered bone matrix NCPs. These studies will advance our knowledge of the fundamental biochemical mechanisms involved in osteogenesis. This fundamental knowledge will be useful in understanding the basic causes of certain genetic and systemic diseases that affect bone.